1. Field of the Invention
The present invention relates to a semiconductor device and a method of forming the same. More specifically, the present invention is directed to magnetic memory devices and methods of forming the same.
2. Description of Related Art
Magnetic memory devices write or erase data using magnetic fields. Magnetic memory devices are high-speed readable and writable and freely rewritable memory devices. Magnetic memory devices are non-volatile memory devices that continuously hold their stored data even when their power supplies are interrupted.
A unit cell of a magnetic memory device mainly uses a magnetic tunnel junction (MTJ) pattern as data storage. The MTJ pattern includes two ferromagnetic substances and a dielectric substance interposed therebetween. Resistance of the MTJ pattern varies with magnetization directions of the two ferromagnetic substances. Assuming that a resistance when the magnetization directions are identical to each other is R1 and a resistance when they are different from each other is R2, the resistance R1 is lower than the resistance R2. A difference between currents flowing through the MTJ pattern, based on the resistance variation, is sensed to determine whether data stored in a magnetic memory cell is logic “1” or “0”.
A typical magnetic memory device includes a digit line and a bitline for inducing a magnetic field applied to an MTJ pattern. The digit line and the bitline are intersected and are disposed under and over the MTJ pattern, respectively.
FIG. 1 is a top plan view of a conventional magnetic memory device, and FIG. 2 is a cross-sectional view taken along a line I-I′ of FIG. 1.
As illustrated in FIG. 1 and FIG. 2, a lower oxide layer 2 is disposed on a substrate 1. A digit line 3 is disposed over the lower oxide layer 2. An intermediate oxide layer 4 is disposed to cover the digit line 3 and the lower oxide layer 2. A contact hole 5 is formed to expose a predetermined area of the substrate 1 through the intermediate oxide layer 4 and the lower oxide layer 2. A contact plug 6 is formed to fill the contact hole 5.
The contact plug 6 is disposed to be spaced apart from one side of the digit line 3. The contact plug 6 is electrically connected to a switching element (not shown, e.g., a source/drain region of a MOSFET) formed below the lower oxide layer 2.
A plurality of bottom electrodes 7 are disposed on the intermediate oxide layer 4 in a parallel direction with the digit line 3. The bottom electrodes 7 are spaced apart from one another. The bottom electrode 7 is connected to the contact plug 6 and extends laterally to cover the the digit line 3. The digit line 3 and the bottom electrode 7 are isolated by the intermediate oxide layer 4. A magnetic tunnel junction (MTJ) pattern 11 is disposed on the bottom electrode 7. The MTJ pattern 11 is aligned over the digit line 3. The bottom electrode 7 is connected to an entire top surface of the contact plug 6 as well as an entire bottom surface of the MTJ pattern 11.
The MTJ pattern 11 includes a first magnetic layer 8 and a second magnetic layer 10, stacked in that order, and a dielectric layer 9 interposed therebetween. A magnetization direction of the first magnetic layer 8 is fixed, and a magnetization direction of the second layer 10 freely varies with external magnetic fields.
An upper oxide layer 12 is disposed to cover an entire surface of the substrate 1. A top surface of the upper oxide layer 12 is level with a top surface of the MTJ pattern 11, and the top surface of the MTJ pattern 11 is exposed.
A bitline 13 is disposed on the upper oxide layer 12 to cross the digit line 3. The bitline 13 is electrically connected to the MTJ pattern 11. The MTJ pattern 11 is disposed at an intersection of the bitline 13 and the digit line 3. For the convenience of description, a digit line 3 and a bitline 13 of FIG. 2 are not shown in FIG. 1.
Magnetic fields established by the bitline 13 and the digit line 3 change a magnetization direction of the second magnetic layer 10. In this case, the first magnetic layer 8 is always fixed. When magnetization directions of the first and second magnetic layers 8 and 10 are identical to each other, a resistance of the MTJ pattern 11 decreases. When the magnetization directions thereof are different from each other, a resistance of the MTJ pattern 11 increases. Thus, the amount of current flowing through the MTJ pattern 11 varies, which is sensed to read data written into the MTJ pattern 11.
The MTJ pattern 11 is interposed between the digit line 3 and the bitline 13 and is electrically connected to the contact plug 6 and the bitline 13. Since the contact plug 6 is laterally spaced apart from the digit line 3, the bottom electrode 7 is connected to the top surface of the contact plug 7 as well as the bottom surface of the MTJ pattern 11. Due to such a structural cause, the bottom electrode 7 has a large plane area. Thus, the plane area of the bottom electrode 7 may become a significant factor in determining a plane area of a magnetic memory cell.
Conventionally, a photolithographic process may result in misalignment. Therefore, lower or upper patterns formed using the photolithographic process include a region for securing a misalignment margin region (hereinafter referred to as “misalign margin region”). The contact hole 8, the bottom electrode 7, and the MTJ pattern 11 are determined by different photolithographic processes respectively to include a misalign margin region.
A first misalign margin region m1 between the bottom electrode 7 and the MTJ pattern 11 is included in the bottom electrode 7. This is because a plane area of the bottom electrode 7 is smaller than that of the MTJ pattern 11. If the MTJ pattern 11 is misaligned with the bottom electrode 7, a characteristic of the MTJ pattern 11 may be degraded due to a step difference caused by a thickness of the bottom electrode 7. Due to the first misalign margin region m1, the plane area of the bottom electrode 7 increases more and a space 15b between adjacent MTJ patterns 11 may be greater than a space 15a between adjacent bottom electrodes 7.
In view of the fact that the plane area of the bottom electrode 7 is larger than that of the contact hole 5, a second misalign margin region m2 between the bottom electrode 7 and the contact hole 5 may be included in the bottom electrode 7. Due to the second misalign margin region m2, the plane area of the bottom electrode 7 may increase more.
Thus, conventionally, a plane area of a magnetic memory cell increases to impede high integration of a magnetic memory device.